Opening structure of a fuel tank

ABSTRACT

The present invention is directed to an opening structure of a fuel tank having a fuel tank wall made of a plurality of plastic layers with an opening portion formed to be integral with the fuel tank wall. The opening structure includes a cylindrical portion extended from the opening portion outward of the fuel tank wall, an overlapping portion extended from an end of the cylindrical portion to enlarge the diameter of the opening portion and bent at a bent portion to form an outer surface parallel with an opening end surface of the opening portion, and a compressed portion with at least a portion of the overlapping portion compressed in a direction perpendicular to the opening end surface of the opening portion. The opening structure may further include an annular member which is disposed around the opening portion to be in contact with the overlapping portion and the cylindrical portion. The plastic layers may include at least an outer layer, an inner layer and an intermediate layer, and the outermost end of the intermediate layer may be positioned at the compressed portion.

[0001] This application claims priorities under 35 U.S.C. Sec. 119 toNos. 2000-237980 and 2001-153250 filed in Japan on Aug. 7, 2000 and May22, 2001, respectively, the entire contents of which are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an opening structure of a fueltank, more particularly the opening structure of the fuel tank for usein an automotive vehicle. Also, the present invention relates to amethod for producing the fuel tank by forming a fuel tank wall with aplurality of plastic layers through blow molding, and forming an openingportion to be integral with the fuel tank wall.

[0004] 2. Description of the Related Arts

[0005] Recently, a fuel tank mounted on an automobile or the like islikely to be made from plastic material. For example, getting popularnow is a method for forming a fuel tank by the plastic material throughblow molding, and forming an opening portion to be integral with thefuel tank wall. As a result, a plastic fuel tank having an openingportion of a desired structure is getting popular. The structure of theopening portion of the fuel tank as described above is disclosed inJapanese Utility-model Laid-open Publication No. 4-7925, for example. InFIG. 3 of that Publication, disclosed is a prior structure, and in FIG.1, a proposed structure for restraining the height of an openingperipheral wall of the fuel tank. According to the Publication, it isdescribed that engaging portions such as nuts are disposed on a baseportion for mounting a cover member thereon, and engaging parts such asbolts are engaged with the engaging portions to secure the cover memberto a fuel tank body, or fuel tank wall, so that a sufficient capacitycan be obtained in a condition of a limited total height. Also disclosedin Japanese Patent No. 2906701 is the structure similar to thatdisclosed in the above Publication as a prior art.

[0006] With respect to the plastic material forming the fuel tank, aplastic member having a plurality of layers is disclosed in JapaneseUtility-model Laid-open Publication No. 61-83509, for example. In thisPublication, disclosed is a blow molded fuel tank with multiple layers,employing multiple plate members with a plurality of component platesadhered together through binding layers.

[0007] When the plastic made fuel tank is produced as disclosed in theabove Publication No. 61-83509, a plastic member having a plurality oflayers is employed. This plastic member includes a strength holdingmember such as high density polyethylene for holding the strength of thefuel tank, a barrier member for protecting the fuel from passing throughit, and binding material or the like for binding them. By forming thatplastic member through a blow molding method, the fuel tank is produced,together with its opening portion formed simultaneously. When theopening portion is covered by the cover member as disclosed in theaforementioned Publication, the end surface of the opening portion witha plurality of layers may be exposed inside of the fuel tank. In thiscase, therefore, the fuel might be leaked from the strength holdingmember of the outermost layer of the plastic member. In the PublicationNo. 4-7925 as described above, it is proposed to connect them by meansof a connecting member such as a bolt or the like, with a packingdisposed between them. When connecting the cover member with the fueltank, however, the bolt and the packing of high sealing property will beneeded. In this case, even if the packing with a good anti-passingproperty is employed, there might be caused the leak of fuel through theoutermost layer of the plastic member.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to providean opening structure of a fuel tank having a fuel tank wall made of aplurality of plastic layers, to protect the fuel from passing throughthe plastic member at an opening portion of the fuel tank, effectively.

[0009] It is another object of the present invention to provide a methodfor forming a fuel tank wall with a plurality of plastic layers throughblow molding, and forming an opening portion to be integral with thefuel tank wall, to produce a fuel tank having an opening structure toprotect the fuel from passing through the plastic member, effectively.

[0010] In accomplishing the above and other objects, an openingstructure of a fuel tank having a fuel tank wall made of a plurality ofplastic layers with an opening portion formed to be integral with thefuel tank wall. The opening structure includes a cylindrical portionextended from the opening portion outward of the fuel tank wall, anoverlapping portion extended from an end of the cylindrical portion toenlarge the diameter of the opening portion and bent at a bent portionto form an outer surface parallel with an opening end surface of theopening portion, and a compressed portion with at least a portion of theoverlapping portion compressed in a direction perpendicular to theopening end surface of the opening portion.

[0011] The opening structure of the fuel tank may further include anannular member disposed around the opening portion to be in contact withthe overlapping portion and the cylindrical portion.

[0012] The compressed portion may provide an annular groove placedoutward or inward of the opening portion in a radial direction of thecylindrical portion.

[0013] Preferably, the plastic layers includes at least an outer layer,an inner layer and an intermediate layer, and the outermost end of theintermediate layer is positioned at the compressed portion.

[0014] Preferably disposed around the opening portion is an annularmember with a step portion formed inward of the annular member in aradial direction thereof to contact with at least the compressedportion.

[0015] The bent portion may be formed with a lifted wall portionextending parallel with the side surface of the cylindrical portion.

[0016] A method for producing a fuel tank by forming a fuel tank wallwith a plurality of plastic layers through blow molding, and forming anopening portion to be integral with the fuel tank wall may include thesteps of forming a cylindrical portion extended from the opening portionoutward of the fuel tank wall, when the fuel tank wall is formed by blowmolding, forming at least a potion of the cylindrical portion to bebulged outward thereof in a radial direction thereof, to provide abulged portion, pressing the bulged portion to form a bent portion bentat the outward of the opening portion in a radial direction thereof, toform an overlapping portion extended from an end of the cylindricalportion to form an outer surface parallel with an opening end surface ofthe opening portion, and compressing at least a portion of theoverlapping portion to be compressed, to produce a compressed portion.

[0017] In the method as described above, the compressed portion may beformed outward of the opening portion in a radial direction of thecylindrical portion. Or, it may be formed inward of the opening portionin a radial direction of the cylindrical portion.

[0018] In the method as described above, the plastic layers may includeat least an outer layer, an inner layer and an intermediate layer, andthe outermost end of the intermediate layer may be positioned at thecompressed portion.

[0019] In the method as described above, an annular member having a stepportion formed inward of the annular member in a radial directionthereof to contact with at least the compressed portion may be disposedaround the opening portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above stated object and following description will becomereadily apparent with reference to the accompanying drawings, whereinlike reference numerals denote like elements, and in which:

[0021]FIG. 1 is a cross sectional view of a part of an opening structureof a fuel tank according to an embodiment of the present invention;

[0022]FIG. 2 is an enlarged cross sectional view of a part of theopening structure of the fuel tank according to an embodiment of thepresent invention;

[0023]FIG. 3 is a plan view of an annular member for use in the openingstructure of the fuel tank according to an embodiment of the presentinvention;

[0024]FIG. 4 is a cross sectional view of an annular member for use inthe opening structure of the fuel tank according to an embodiment of thepresent invention;

[0025]FIG. 5 is a cross sectional view illustrating a bulging step forforming the opening structure of the fuel tank according to anembodiment of the present invention;

[0026]FIG. 6 is a cross sectional view illustrating a compressing stepfor forming the opening structure of the fuel tank according to anembodiment of the present invention;

[0027]FIG. 7 is an enlarged cross sectional view of a part of an openingstructure of a fuel tank according to another embodiment of the presentinvention;

[0028]FIG. 8 is an enlarged cross sectional view of a part of an openingstructure of a fuel tank according to a further embodiment of thepresent invention;

[0029]FIG. 9 is an enlarged cross sectional view of a part of an openingstructure of a fuel tank according to a yet further embodiment of thepresent invention; and

[0030]FIG. 10 is a cross sectional view of an opening structure of afuel tank according to a yet further embodiment of the presentinvention;

[0031]FIG. 11 is an enlarged cross sectional view of a part of theopening structure according to the embodiment as shown in FIG. 10;

[0032]FIG. 12 is an enlarged cross sectional view of another example ofa part of the opening structure according to the embodiment as shown inFIG. 10;

[0033]FIG. 13 is a plan view of the opening structure according to theembodiment as shown in FIG. 10;

[0034]FIG. 14 is an enlarged cross sectional view of a part of a die forforming the opening structure according to the embodiment as shown inFIG. 10;

[0035]FIG. 15 is a cross sectional view illustrating a bulging step forforming the opening structure according to the embodiment as shown inFIG. 10; and

[0036]FIG. 16 is a cross sectional view illustrating a compressing stepfor forming the opening structure according to the embodiment as shownin FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Referring to FIG. 1, there is illustrated an opening structure ofa fuel tank according to an embodiment of the present invention, a partof which is sectioned and enlarged in FIG. 2. According to the presentembodiment, a fuel tank wall 1 is formed with a plastic member having aplurality of layers through blow molding, and an opening portion 1 h isformed integrally with the fuel tank wall 1. A method for producing itwill be explained later.

[0038] As shown in FIGS. 1 and 2, in the vicinity of the opening portion1 h, there are formed a cylindrical portion 1 e which is extended fromthe opening portion 1 h outward of the fuel tank wall 1, and anoverlapping portion 1 d which is extended from an end of the cylindricalportion 1 e to enlarge the diameter of the opening portion 1 h and bentat a bent portion 1 b to form an outer surface parallel with an openingend surface Sh of the opening portion 1 h. And, at least a portion ofthe overlapping portion 1 d is compressed in a direction perpendicularto the opening end surface Sh of the opening portion 1 h, to form acompressed portion 1 c. In FIG. 1, hatching to the plastic memberconstituting the fuel tank wall 1 is omitted to show the structureclearly.

[0039] As illustrated in FIG. 2, the plastic member constituting thefuel tank wall 1 is the one with multiple layers, that includes an outerlayer Po and an inner layer Pi, both of which are formed by the strengthholding member, and an intermediate layer B which is formed with thebarrier material and disposed between them, to be bound together byadhesive plastics. As for the strength holding member employed in thepresent embodiment, ultra high polymeric (high density) polyethylene isused. As for the barrier material, EVOH (i.e., plastic with ethylene andvinyl-alcohol co-polymerized) is used, for example. According to thepresent invention, however, the materials are not limited to those asdescribed above, but may be employed any materials which can protect thefuel of gasoline or the like from being passed, to provide effectivegas-barrier property.

[0040] According to the present embodiment, the bent portion 1 b is bentinward (toward the opening) as shown in FIG. 2, so that even if the fuelpassed through the inner layer Pi, it could be blocked by theintermediate layer B at the bent portion 1 b, effectively. And, thecompressed portion 1 c is formed to provide an annular groove, where thethickness of the outer layer Po is formed relatively thin, comparingwith the thickness at the cylindrical portion 1 e. Thus, the thicknessof the outer layer Po is formed to be thin at the compressed portion 1c, so that the passage has been made narrow, thereby to provide aresistance when the fuel is introduced from an opening end surface 1 p.On the contrary, according to the opening structure without thecompressed portion 1 c formed therein, the opening end surface(corresponding to “1 p” in FIG. 2) of the plastic member with multiplelayers can be directly communicated with the outer space. Therefore,even in the case where a seal member (not shown) was disposed between acover member 4 and an annular fixing member 5, the fuel might passthrough the outer layer Po. Theoretically, some fuel might be introducedfrom the opening end surface 1 p to pass through the thin portion of thecompressed portion 1 c, and reach the bent portion 1 b, according to thepresent embodiment, but the amount of fuel is so small as to besubstantially negligible.

[0041] Furthermore, an annular member 2 is placed to surround theopening portion 1 h, and fixed to the same with its inner side abuttingon the outer side surface of the cylindrical portion 1 e, and with itstop end surface abutting on the lower surface of the overlapping portion1 d. The annular member 2 is made of plastic, with a c-shaped crosssection opened to the outside in a radial direction, and formed as shownin FIGS. 3 and 4. That is, a recess 2 r is formed around its outerperiphery, and opposite end surfaces in its axial direction are formedto be parallel with each other. As shown in FIG. 4, the annular member 2is formed with a threaded portion 2 s, on its outer side surface at itsupper portion. And, as shown in FIG. 3, the annular member 2 is formedwith a plurality of communication holes 2 c opened in the axialdirection, around its whole periphery. The annular member 2 is placed soas to surround the opening portion 1 h, and abut on the cylindricalportion 1 e and the overlapping portion 1 d, so that it is bound withthe outer layer Po in a body. In other words, when the annular member 2is formed, the plastic material is introduced into the communicationholes 2 c, so that the annular member 2 is secured to the cylindricalportion 1 e not to rotate relative thereto. The outer layer Po isextended to cover a portion of the outer peripheral end of the annularmember 2, to form an engaging portion 1 f.

[0042] The opening portion 1 h as constituted above has the compressedportion 1 c to provide an annular groove, which receives a sealingmember 3 made of rubber or the like as shown in FIG. 1. Therefore, afterthe cover member 4 is placed on the sealing member 3, the fixing member5 having a threaded portion inside thereof is mounted on the covermember 4, and engaged with the threaded portion 2 s of the annularmember 2. Consequently, the cover member 4 is tightly fixed to the uppersurface of the overlapping portion 1 d through the sealing member 3.When the fixing member 5 is screwed, the annular member 2 is notrotated, because the annular member 2 is secured to the cylindricalportion 1 e not to rotate relative thereto. According to the presentembodiment, portions through which the fuel in the tank may becommunicated with the outside of the tank, are only the portions wherethe sealing member 3 abuts on the cover member 4 and overlapping portion1 d, and the portion where the outer layer Po out of the multiple layerswas formed relatively thin, when the compressed portion 1 c was formed.As a result, the fuel is effectively prevented from passing through theopening portion of the fuel tank wall 1. Particularly, a good sealingproperty can be ensured, because a profile irregularity has beenimproved to provide a smooth surface on the bottom surface of thecompressed portion 1 c.

[0043]FIGS. 5 and 6 illustrate an example of a process for producing thefuel tank having the opening structure as described above. At theoutset, according to a forming process as shown in FIG. 5, placedbetween dies D1 and D2 is a multi-layer parison PT made of the plasticmember with multiple layers. As shown by two-dot chain lines in FIG. 5,the die D1 is supported to move perpendicularly to the die D2. The diesD1 and D2 are formed insides thereof with a protrusion D1 p and a recessD2 r, respectively. The protrusion D1 p is formed to provide thecompressed portion 1 c as shown in FIG. 2, and the recess D2 r is formedto receive the annular member 2. Furthermore, a spacer SP is disposed tomove back and forth perpendicularly to the axis of the die D1 (i.e., theaxis of the opening portion 1 h). The spacer SP is adapted to hold theannular member 2 within the recess 2 r of the annular member 2 in apressing process. And, the spacer SP is adapted to move perpendicularlyto the axis of the die D1 in accordance with a movement of the die D1.Also, it is so arranged that the air pressure or hydraulic pressure issupplied into the multi-layer parison PT through a conduit (not shown).

[0044] Accordingly, with the air pressure or hydraulic pressureintroduced into the multi-layer parison PT, the die D1 is moved relativeto the die D2 toward the annular member 2. Simultaneously, in accordancewith the movement of the die D1, the spacer SP is moved in the directionperpendicular to the axis of the die D1, and held in the recess 2 r ofthe annular member 2. As a result, the multi-layer parison PT is bulgedoutwardly as shown in FIG. 5, while the portion abutting on the annularmember 2 is restricted from being bulged outwardly to form thecylindrical portion 1 e. Furthermore, the bent portion 1 b and theoverlapping portion 1 d are formed accurately, as shown in FIG. 6. Also,the overlapping portion id is compressed by the protrusion D1 p of thedie D1 to form the compressed portion 1 c. At the same time, formed is acover portion 1 gas shown in FIG. 6, which will be removed later.

[0045]FIG. 7 illustrates the opening structure of the fuel tankaccording to another embodiment of the present invention, wherein all ofthe overlapping portion 1 d is compressed to form the overlappingportion 1 d as a whole into the compressed portion. According to thisembodiment, therefore, the profile irregularity of the outer surface(upper surface in FIG. 7) of the overlapping portion id is improved toprovide a smooth surface, so that a good sealing property can beobtained. Furthermore, if the profile irregularity of the lower surfaceof the cover member 4 is proper, a good sealing property can be obtainedwithout any sealing member.

[0046]FIG. 8 illustrates the opening structure of the fuel tankaccording to a further embodiment of the present invention, wherein theannular member 2 is formed on its upper surface with a protrusion 2 t,so that when the overlapping portion 1 d is compressed, a compressedportion 1 cu is formed on its lower surface. According to thisembodiment, thickness of the outer layer Po is made thinner at thecompressed portion 1cu to narrow the passage, whereby the resistance isapplied to the fuel when introduced from the opening end surface 1 p.Also, the profile irregularity of the outer surface (upper surface inFIG. 8) of the overlapping portion 1 d above the compressed portion 1 cuis improved to provide a smooth surface, so that a good sealing propertycan be obtained.

[0047]FIG. 9 illustrates the opening structure of the fuel tank furthermodified to the embodiment as shown in FIG. 8, wherein the cover portion1 g remained after the forming process can be removed easily. Whencompressed, a compressed portion 1 ci is formed on the overlappingportion 1 d at the inner side of the opening portion 1 h in its radialdirection. By applying shearing force onto the thin compressed portion 1ci, he cover portion 1 g can be removed easily.

[0048] Next will be explained about a yet further embodiment of thepresent invention with reference to FIGS. 10-16, wherein the outermostend of the intermediate layer B is positioned at the compressed portion1 c. In FIGS. 10-16, the elements which are substantially the same asthose shown in FIGS. 1-9 are designated by the same reference numeralsas the numerals in FIGS. 1-9. Referring to FIGS. 10-13, the fundamentalstructure of the present embodiment is substantially the same as thatshown in FIGS. 1 and 2, except for the position of the outermost end ofthe intermediate layer B, and the configurations of fuel tank wall 11(and elements thereof), annular member 12 (and elements thereof) andannular fixing member 15, which are equivalent to those describedoriginally, and designated by corresponding reference numerals with ten(10) preceding them.

[0049] As shown in FIGS. 10 and 11, the outermost end of theintermediate layer B is positioned at a compressed portion 11 c. And, alifted wall portion 11 k is formed to extend from a bent portion 11 b inparallel with the side surface of a cylindrical portion 11 e.Consequently, an annular groove is formed on the compressed portion 11 cinside of the lifted wall portion 11 k. On the contrary, as shown inFIG. 12, a step which is formed when the wall 11 is compressed, withoutforming the lifted wall portion 11 k, may serve as the compressedportion 11 c to open outward. The annular member 12 is placed tosurround the opening portion 11 h made of the plastic member forming thefuel tank wall 11, and fixed to the same. The annular member 12 is madeof plastic, with its inner side abutting on the outer side surface ofthe cylindrical portion 11 e, and with its upper end surface abutting onthe lower surface of the overlapping portion 11 d. And, the annularmember 12 is formed at its inside with a step portion 12 d to abut onthe bent portion 11 b (and the lifted wall portion 11 k as shown in FIG.11 in this embodiment). The annular member 12 is formed at its outsidewith a threaded portion 12 s, and formed with a recess 12 r on one endsurface in its axial direction (i.e., lower end surface as shown in FIG.11).

[0050] With respect to the opening portion 11 h as constituted above,the compressed portion 11 c provides an annular groove, which receivesthe sealing member 3 as shown in FIG. 11. Therefore, after the covermember 4 is placed on the sealing member 3, the annular fixing member 15having a threaded portion inside thereof is mounted on the cover member4, and engaged with the threaded portion 12 s of the annular member 12.Consequently, the cover member 4 is tightly fixed to the upper surfaceof the compressed portion 11 c through the sealing member 3. Accordingto the present embodiment, portions through which the fuel in the tankmay be communicated with the outside of the tank, are only the portionswhere the sealing member 3 abuts on the cover member 4 and compressedportion 11 c, and the portion where the outer layer Po out of themultiple layers was formed relatively thin, when the compressed portion11 c was formed, and particularly, the outermost end of the intermediatelayer B is positioned at a compressed portion 11 c, so that a passage isformed narrow. As a result, the fuel is effectively prevented frompassing through the opening portion of the fuel tank 11. Additionally, agood sealing property can be ensured, because a profile irregularity hasbeen improved to provide a smooth surface on the bottom surface of thecompressed portion 11 c.

[0051]FIG. 14 illustrates dies for use in producing the fuel tank havingthe opening structure as shown in FIGS. 10 and 11, and FIGS. 15 and 16illustrate an example of the process for producing it. In the followingdescription, structural elements of dies equivalent to those describedoriginally are designated by corresponding reference numerals with (o)following them. As shown in FIG. 14, a die D1 o is supported to movevertically, while a die D2 o is supported to move horizontally. The diesD1 o and D2 o are formed insides thereof with a protrusion D1 po and arecess D2 ro, respectively. The protrusion D1 po is formed to providethe compressed portion 11 c as shown in FIG. 11, and the recess D2 ro isformed to receive the threaded portion 12 s of the annular member 12. InFIG. 14, the formed or finished opening portion 11 h of the fuel tankwall 11 is shown.

[0052] In a forming process as shown in FIG. 15, after the annularmember 12 is placed between the dies D1 o and D2 o, the multi-layerparison PT made of the plastic member with multiple layers (three layersin this embodiment). And, it is so arranged that the air pressure orhydraulic pressure is supplied into the multi-layer parison PT.Accordingly, with the air pressure or hydraulic pressure introduced intothe multi-layer parison PT, the die D1 o is moved relative to the die D2o toward the annular member 12 as indicated by a blank arrow in FIG. 15.As a result, the multi-layer parison PT is bulged outwardly as shown inFIG. 15, while the portion abutting on the annular member 12 isrestricted from being bulged outwardly to form the cylindrical portion11 e. Furthermore, the bent portion llb and the overlapping portion 11 dare formed accurately, as shown in FIG. 16. Also, the overlappingportion 11 d is compressed by the protrusion D1 po of the die D1 o toform the compressed portion 11 c and the lifted wall portion 11 k. Atthe same time, formed is a cover portion 11 g as shown in FIG. 16, whichwill be removed later.

[0053] It should be apparent to one skilled in the art that theabove-described embodiments are merely illustrative of but a few of themany possible specific embodiments of the present invention. Numerousand various other arrangements can be readily devised by those skilledin the art without departing from the spirit and scope of the inventionas defined in the following claims.

What is claimed is:
 1. An opening structure of a fuel tank having a fueltank wall made of a plurality of plastic layers, with an opening portionformed to be integral with said fuel tank wall, comprising: acylindrical portion extended from said opening portion outward of saidfuel tank wall; an overlapping portion extended from an end of saidcylindrical portion to enlarge the diameter of said opening portion andbent at a bent portion to form an outer surface parallel with an openingend surface of said opening portion; and a compressed portion with atleast a portion of said overlapping portion compressed in a directionperpendicular to the opening end surface of said opening portion.
 2. Theopening structure of the fuel tank according to claim 1, furthercomprising an annular member disposed around said opening portion to bein contact with said overlapping portion and said cylindrical portion.3. The opening structure of the fuel tank according to claim 1, whereinsaid compressed portion provides an annular groove placed outward ofsaid opening portion in a radial direction of said cylindrical portion.4. The opening structure of the fuel tank according to claim 1, whereinsaid compressed portion provides an annular groove placed inward of saidopening portion in a radial direction of said cylindrical portion. 5.The opening structure of the fuel tank according to claim 1, whereinsaid plastic layers includes at least an outer layer, an inner layer andan intermediate layer, and wherein the outermost end of saidintermediate layer is positioned at said compressed portion.
 6. Theopening structure of the fuel tank according to claim 5, furthercomprising an annular member disposed around said opening portion, saidannular member having a step portion formed inward of said annularmember in a radial direction thereof to contact with at least saidcompressed portion.
 7. The opening structure of the fuel tank accordingto claim 6, wherein said bent portion is formed with a lifted wallportion extending parallel with the side surface of said cylindricalportion.
 8. The opening structure of the fuel tank according to claim 5,wherein said bent portion is formed with a lifted wall portion extendingparallel with the side surface of said cylindrical portion.
 9. A methodfor producing a fuel tank by forming a fuel tank wall with a pluralityof plastic layers through blow molding, and forming an opening portionto be integral with said fuel tank wall, comprising: forming acylindrical portion extended from said opening portion outward of saidfuel tank wall, when said fuel tank wall is formed by blow molding;forming at least a potion of said cylindrical portion to be bulgedoutward thereof in a radial direction thereof, to provide a bulgedportion; pressing said bulged portion to form a bent portion bent at theoutward of said opening portion in a radial direction thereof, to forman overlapping portion extended from an end of said cylindrical portionto form an outer surface parallel with an opening end surface of saidopening portion; and compressing at least a portion of said overlappingportion to be compressed, to produce a compressed portion.
 10. Themethod according to claim 9, wherein said compressed portion is formedoutward of said opening portion in a radial direction of saidcylindrical portion.
 11. The method according to claim 9, wherein saidcompressed portion is formed inward of said opening portion in a radialdirection of said cylindrical portion.
 12. The method according to claim9, wherein the blow molding is performed, with an annular member placedaround said opening portion, to form said cylindrical member inside ofsaid annular member.
 13. The method according to claim 12, wherein saidcompressed portion is formed outward of said opening portion in a radialdirection of said cylindrical portion.
 14. The method according to claim12, wherein said compressed portion is formed inward of said openingportion in a radial direction of said cylindrical portion.
 15. Themethod according to claim 9, wherein said plastic layers includes atleast an outer layer, an inner layer and an intermediate layer, andwherein the outermost end of said intermediate layer is positioned atsaid compressed portion.
 16. The method according to claim 15, whereinan annular member disposed around said opening portion, said annularmember having a step portion formed inward of said annular member in aradial direction thereof to contact with at least said compressedportion.
 17. The method according to claim 16, wherein said bent portionis formed with a lifted wall portion extending parallel with the sidesurface of said cylindrical portion.
 18. The method according to claim15, wherein said bent portion is formed with a lifted wall portionextending parallel with the side surface of said cylindrical portion.